Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $43.67   10.642%   $48.3174   $48.32   $48.30   $48.30  
  Purchase #2 $233.55   9.657%   $256.1039   $256.10   $256.10   $256.10  
  Purchase #3 $168.77   10.676%   $186.7879   $186.79   $186.80   $186.80  
  Purchase #4 $186.58   13.168%   $211.1489   $211.15   $211.15   $211.10  
  Purchase #5 $229.30   8.114%   $247.9054   $247.91   $247.90   $247.90  
  Purchase #6 $135.36   8.651%   $147.07   $147.07   $147.05   $147.10  
  Purchase #7 $71.62   9.663%   $78.5406   $78.54   $78.55   $78.50  
  7 purchase totals = $1,068.85       $1,175.8741   $1,175.88   $1,175.85   $1,175.80